Radioactivity survey on Godakawela gem field in Sri Lanka; to identify the origin of the unknown radioactive mineral

Abstract

Sri Lanka is well known for high-quality gemstones and approximately 25% of the total land area is liable for potential gem fields. Despite of that identification of new promising gem bearing areas is essential. In Sri Lanka, such investigations are mostly based on the sedimentological and geochemical analysis rather than in-situ radioactive surveys which are common in global contest. Information derived from sporadic studies and gem miners revealed that Godakawela gem field has interesting radioactiveness. Hence, this study focuses on the presence of radioactive minerals, their distribution and the origin of the gem deposit in Godakawela gem field. The ambient gamma dose rate was measured by the plastic scintillation detector from 40 points in random walk mode and gamma energy value was recorded in the NaI scintillation detector. Results have proved that Godakawela region has high radioactiveness with respect to the average baseline value Sri Lanka. The radioactive anomaly pattern and the presence of zircon and tourmaline like associated minerals, together with the surrounded geological aspects have suggested that the radioactive minerals may have a primary origin. Further, X-ray diffractogram shows the corresponding peaks for euxenite as a radioactive mineral but to confirm recrystallization analysis with heat treatment is needed.

Metamict Fergusonite from Kolonna and Masimbula, Sri Lanka

“…The location is well known for its radioactive minerals (Kuruppu et al, 2020). We may speculate that our sample corresponds to the "radioactive mineral" of Kuruppu et al (2020;see Fig. 5 in that paper) from the same location, which was suspected as euxenite based on preliminary results of NaI scintillation detector and X-ray diffraction measurements.…”

“…The quarry was operated for gem mining predominantly more than two decades ago. The location is well known for its radioactive minerals (Kuruppu et al, 2020). We may speculate that our sample corresponds to the "radioactive mineral" of Kuruppu et al (2020;see Fig.…”

“…The mere detection of Ra-and Th-related radioactivity does not help much, as such pattern is obtained from any Thcontaining mineral. Broad humps in the X-ray diffraction pattern at d  2.98 Å and d  1.77 Å (observed at 2 angles of 30° and 51.5° when Cu-K radiation is used; Kuruppu et al, 2020) cannot be assigned to a crystalline mineral. Mathavan and Fernando, 2001;Kröner et al, 2013;Nasdala et al, 2017).…”